How To Test a Ford Focus MAF Sensor

How To Test a Ford Focus MAF Sensor

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One of the more common Ford Focus problems centers around your mass air flow sensor. The Focus MAF Sensor is a part of your intake system, and is utilized to read the incoming air charge. By analyzing the volume of air as well as reading the air temperature, your Focus Powertrain Control Module (PCM) can manage the fuel delivery properly.

When your Focus MAF sensor goes bad, the engine computer won’t have the right reference. Without this signal there’s little chance of your 2.0 liter Zetec engine running right. Today I’ll be showing you how to test the Focus MAF sensor in a 2004 2.0 liter Ford Focus LX.

One of the first indicators of this Ford Focus problem is your check engine light. This light is a part of your On Board Diagnostic system, and it known as the OBDII trouble code indicator. When you see your Ford check engine light turn on, you’ll need a proper OBDII scan tool to retrieve your trouble code.

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This trouble code is a five digit alphanumeric code that will tell you what the problem is. When your 2.0 liter Ford MAF sensor fails on you, there’s a few trouble codes that can indicate an issue.

These codes can range from lack of signal, or the signal being out of range. Whether your Ford engine computer doesn’t see a signal, or it’s receiving a signal that is outside what it’s expecting, you can use this guide to test your air flow meter.

How Do I know my Focus MAF sensor is bad?

There’s a few different ways that your mass airflow meter can fail or become fouled. Because this unit depends on unobstructed air flow as well as a thermistor to determine engine temperature, over time it can fail. When this happens you’re going to see several Ford Focus problems crop up.

One of the most common Ford Focus issues is your engine idle. Because your mass air flow meter is not working correctly, it’s going to cause a poor idle. Your engine speed may vary at idle or fluctuate. Your Focus may also have no power or hesitate when accelerating. This is caused by improper fuel delivery because your Ford Focus engine computer doesn’t know what’s going on.

Although you can use a scan tool to check your trouble code, the easiest way to check MAF operation is to unplug it while your engine is running. If your engine doesn’t sound any worse or there’s little change with your MAF unplugged, chances are it’s bad.

Testing the Focus MAF Sensor for power

In order to test your air flow meter, you’ll need to insert your ignition and turn to the “ON” position. This powers the engine sensors in your 2.0 liter engine bay, and allows you to check your engine harness.

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Your Focus MAF Sensor is connected to the intake piping leading out of your throttle body. It’s held onto your MAF housing by two screws which can be undone to remove or replace your Focus MAF Sensor.

Because we are starting with the power and ground circuits to your Focus MAF, you will need a digital multimeter. This device reads the voltage from your engine harnesses and sensors, and is one of the most important troubleshooting tools you could ever own.

Depending on your model Ford Focus, you may have a four or six wire MAF sensor. The difference between the two is the Intake Air Temperature sensor. If you happen to own a Ford Focus MAF sensor with four wires, this means your IAT is located in your intake piping. If your MAF has six wires the IAT is integrated and you can test it at the same time.

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The power wire for your Focus MAF sensor leads to PIN A in our MAF diagram. Don’t forget that you are testing the ENGINE side. Reference our Focus MAF wiring schematic to see which wire you will be testing for 12 volts.

Ground is the next signal you’ll need to check for. There’s two ground circuits, one supplied by the engine computer, and the other by the chassis.

To check for ground reverse the polarity of your leads and connect the red lead of your multimeter to the positive wire on your battery. Now gently probe the ENGINE side of the harness at the wire leading to PIN B. This is your chassis ground and the next wire to check is the one that comes to PIN C. This ground is supplied by your Powertrain Control Module or PCM.

The last wire to check on your Focus MAF sensor happens to be the air flow signal wire. This guy is marked at the wire leading to PIN D. You can go about this test one of two ways, you can either reconnect the MAF connector and pierce the D wire with your multimeter, or plug in a OBDII scan tool to read the real time events.Test a Ford Focus MAF Sensor 4

Either way when you are testing the voltage from your MAF signal wire, you want to make sure that there’s no gaps or spikes in the voltage. This voltage signal should rise along with engine speed, and fall retrospectively. Testing this part of your Focus is easy to do, but it can also be dangerous.

Start your engine and wait until it’s fully warmed up. Now carefully probe PIN D without getting close to the engine, the drive belts or the cooling fans. This signal should hover or remain steady at idle. Record this voltage and this is known as your MAF signal BASE.

Now rev your engine or increase engine speed to around 2000 RPM, you should see this voltage rise. It should rise evenly and without spikes or gaps in it. If you see any abnormalities it’s time to get yourself a MAF replacement. We sell this replacement mass air flow meter with and without the housing.

Have any questions about our Focus MAF Sensor DIY tutorial? Leave us a comment below and let us know!

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